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Any state other than the ground state of an atom or molecule.

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Cis-Trans Isomerism

A type of geometrical isomerism related to the angles between like ligands.

Forbidden Zone

A relatively large energy separation between an insulator's highest filled electron energy band and the next higher energy vacant band. Beginning in the fourth energy level, a set of seven degenerate orbitals per energy level, higher in energy than s, p, and d orbitals of the same energy level.

Open Sextet

Refers to species that have only six electrons in the highest energy level of the central element (many Lewis acids).

Crystalline Solid

A solid characterized by a regular, ordered arrangement of particles.


Absorption of high energy radiation by a substance and subsequent emission of visible light.

Supersaturated Solution

A solution that contains a higher than saturation concentration of solute, slight disturbance or seeding causes crystallization of excess solute.


Display of component wavelengths (colours) of electromagnetic radiation.

Le Chatelier's Principle

States that a system at equilibrium, or striving to attain equilibrium, responds in such a way as to counteract any stress placed upon it.
If a stress (change of conditions) is applied to a system at equilibrium, the system shifts in the direction that reduces stress.

Lewis Dot Formula (Electron Dot Formula)

Representation of the core of a molecule, ion or formula unit by showing atomic symbols and only outer shell electrons.

Net Ionic Equation

Equation that results from canceling spectator ions and eliminating brackets from a total ionic equation.